Hops contribute two basic flavor notes to beer (including ale): bitterness, contributed by the isohumulones and hulupones and other minor bitter acids; and aromatic notes, contributed by hop oil constituents (generically considered to be terpenoids for the purposes of this specification). Traditionally, hops high in alpha acids are added at the outset of wort boiling, to convert the alpha acids to bitter hop acids. Aromatic hops are added late in the boil, after the boil, or even after fermentation, to incorporate the terpenoid constituents responsible for giving beer a so-called hoppy aroma and flavor. This flavor is particularly characteristic of the finest premium beers, where the inefficiencies of late hopping (in which the alpha acids are poorly utilized) are not a problem because the beer is marketed at premium prices.
For example, a premium beer is typically made by adding a high alpha hop or hop extract at the beginning of wort boil, and adding aroma hops towards the end and/or after the boil. Even then, a large portion of the aroma is lost in boiling or subsequent fermentation. A hop oil is a mixture of perhaps two hundred compounds, of which terpene hydrocarbon, alcohols, ketones, some esters, and epoxides are important constituents. The balance among these constituents controls the flavor and aromatic qualities of the beer. In conventional hopping, as described above, reproducibility is only marginal at best, for not only is there lot to lot variation in the hops, uncertainty as to the amount of the various terpenoids which will be lost in the fermentation and storage of the beer (and the proportions lost are related to the degree of water solubility of the terpenoids), but the aroma and flavor is also related to the length of time the hops have been stored. Freshly harvested hops are known to give a different flavor than year-old hops.
Accordingly, efforts to overcome these control problems have been made in recent years by carefully extracting hops aromas with carbon dioxide, by making emulsions of these oils and aroma using Polysorbate 80.TM. (polyoxyethylene (20) sorbitan mono-oleate), and also by adding the oils as a portion of isohumulones as described as an option in U.S. Pat. No. 3,486,906 (Todd). Each of these efforts has its shortcoming. The Polysorbate emulsions introduce Polysorbate into the beer, which can become rancid and objectionable in such a delicately flavored system as well as potentially requiring label disclosure. The isohumulone emulsions may not be stable, and the hop oil may float out, so that it does not dissolve in the beer. Gum emulsions present the same potential difficulty and uncertainty. So do dispersions of hop oil on a water-soluble substrate, such as dextrose. It is well known to the art that spice flavorings may be dispersed on dextrose, and the dispersions added to a food such as sausage as a flavoring. Such a system has never been practical for hop flavors, since the oils and bitter acids tend to float out in the beer, and are not uniformly dissolved. Thus both efficiency is lost, and objectionable "hot spots" of flavor may be present.
It must be taken into account that hop oil is present in beer at levels of about one part per million, and the individual constituents at the part per billion level. A beer without some hop oil tends to be grainy or cardboardy; with these constituents it can be aromatic, floral, full bodied, etc., with a masking of the grainy notes and much more exciting to the palate and nose. However, when the oil in total approaches two parts per million, or its most readily detected constituents more than perhaps 200 or 300 parts per billion, it can be objectionable. And, compounding the difficulty of control is the lack of any precise assay for the part per billion level of specific terpenoids in the beer. Organoleptic evaluation is the only tool, and it is of course highly subjective and imprecise.
Accordingly, a method by which a carefully tailored hop oil, of known terpenoid composition, can be reproducibly and economically introduced into the beer, without introducing non-hop constituents or resulting in objectionable flavors, will be of great advantage to the art of brewing. It is an object of this invention to provide such a method.
Of particular interest is the application of this invention to the micro-brewer or home brewer, who does not pasteurize his beer. When such brewers add hops to their beer following fermentation, to achieve a "dry hop" character, microorganisms are introduced which can spoil the beer. The flavors of this invention are sterile, and thus permit dry hopping without danger of infection.